The invention relates to a method and apparatus for directional boring in rocky formations using an onboard sonde for controlling the direction of the bore.
Directional boring apparatus or trenchless drills for making holes through soil are well known. The directional borer generally includes a series of drill rods joined end to end to form a drill string. The drill string is pushed or pulled though the soil by means of a powerful device such as a hydraulic cylinder. See McDonald et al. U.S. Pat. No. 4,694,913, Malzahn, U.S. Pat. Nos. 4,945,999 and 5,070,848, and Cherrington, U.S. Pat. No. 4,697,775 (RE 33,793). The drill string may be pushed and rotated at the same time as described in Dunn, U.S. Pat. No. 4,953,633 and Deken, et al., U.S. Pat. No. 5,242,026. A spade, bit or head having one or more angled faces configured for boring is disposed at the end of the drill string and may include an ejection nozzle for water or drilling mud to assist in boring.
In one known directional boring system, the drill bit is pushed through the soil without rotation in order to steer the tool by means of the angled face, which is typically a forwardly facing sloped surface. For rocky conditions, a row of teeth may be added to the drill bit and the bit operated in the manner described in Runquist et al. U.S. Pat. No. 5,778,991. Other toothed bits for directional boring through rock are shown in European Patent Applications Nos. EP 0 857 852 and EP 0 857 853, Cox U.S. Pat. No. 5,899,283, Skaggs U.S. Pat. No. 5,647,448 and Stephenson U.S. Pat. No. 5,799,740. Steering systems for use with these devices require keeping track of the angle of rotation of the sloped face of the bit and/or the teeth.
According to another known system, a transmitter or sonde mounted in a tubular housing is mounted behind and adjacent to the bit and sends a signal that indicates the angle of rotation of the bit. The sonde is mounted in a predetermined alignment relative to the steering portion of the bit. Since the sonde housing is generally made of steel, a series of longitudinal slots or windows are provided through the wall of the sonde housing to permit transmission of the signal. See generally Mercer U.S. Pat. Nos. 5,155,442, 5,337,002, 5,444,382 and 5,633,589, Hesse et al. U.S. Pat. No. 5,795,991, and Stangl et al. U.S. Pat. No. 4,907,658. Mounting of the sonde in its housing has been accomplished by end loading as illustrated by the foregoing patent to Stangl et al. or through a side opening which is closed by a door or cover during use, as illustrated in Lee et al. U.S. Pat. Nos. 5,148,880 and 5,253,721.
Prior attempts to use sondes in horizontal directional boring apparatus, particularly of the type for drilling consolidated rock formations, have proven less than ideal. Breakage of the sonde is to be avoided because sondes are difficult and expensive to replace. The sonde housing cover in side-loading sonde housings is prone to failure. The bolts used to secure the cover often loosen or break off as a result of the abrasion and stress applied to the sonde housing during boring, and the door or cover may work loose or collapse inwardly, crushing the sonde. A need remains for a more secure side-loading sonde housing which is nonetheless easy to open and close when necessary.
A need also persists for a directional boring system specifically adapted to horizontal boring through rocky formations, i.e., wherein the drilling head efficiently bores through consolidated rock formations which ordinary duckbill type bits are unable to penetrate. This can be particularly troublesome when mixed conditions are encountered during a bore, for example, the first portion of the bore is made through soft soil, but an unexpected rock formation is encountered. The connection between the bit and sonde housing should pass torque without undue strain, resist the unavoidable abrasion of surface metal that occurs during use, and yet readily permit disconnection, such as at the terminal end of a bore, at which point the drilling head (including both sonde housing and bit) is typically removed so that the drill string can be used to pull a pipeline back through the completed bore as it withdraws.
Threaded connections between the bit and the sonde housing are secure and shielded from abrasion, but difficult to disengage manually due to the high torque applied to the bit during operation. Bolts used to attach the bit to a sonde housing are exposed to abrasion and tend to loosen. It is also desirable to provide a bit which can be rebuilt and used several times, doubling or tripling the service life of the unit. The present invention addresses these concerns.
The present invention provides an improved apparatus for directional boring and in particular an improved system for boring through hard and rocky substrates frequently encountered when boring under obstacles such as roadways. According to one aspect of the invention, a directional drilling apparatus includes a drilling head having a front face angled relative to the lengthwise axis of the tool and configured for steering the drilling apparatus, a housing having an internal chamber for mounting an electronic locating device therein rearwardly of the drilling head for transmitting a signal indicating the orientation of the angled face of the drilling head, and a joint at which the drilling head is removably mounted to the housing of the locating device. The joint includes a splined connection for passing torque from the sonde housing to the bit and an interlock mechanism which mechanically secures the bit to the sonde housing in a manner permitting the bit to be manually removed from the housing without undue difficulty.
According to a preferred form of the invention, the interlock mechanism includes a projection, which may be the front end of the sonde housing or the rear end of the bit, and a socket into which the projection closely fits, which socket is formed on the other of the front end of the sonde housing or the rear end of the bit. The projection has a first opening having a lengthwise axis which lies in a plane substantially perpendicular to the axis of rotation of the drilling head, and a wall defining the socket has a second opening therein having a lengthwise axis which lies in a plane substantially perpendicular to the axis of rotation of the drilling head and which is brought into alignment (or near alignment, as described hereafter) with the first opening when the projection is fully inserted into the socket. A retainer is sized for insertion into the aligned openings. The retainer is preferably a pin or generally tubular insert that can be compressed from a relaxed state diameter to a retaining diameter at which an outer circumferential surface of the retainer tightly engages inner surfaces of the openings and holds the bit in engagement with the sonde housing.
The splined connection between the bit and the sonde housing preferably includes a series of longitudinal, spaced splines in one of the rear end of the bit or the front end of the sonde housing, and a corresponding series of longitudinal, spaced grooves in the other of the rear end of the bit or the front end of the sonde housing. Since the bit and housing must be keyed to one another so that the position of the sonde is in a known alignment relative to the cutting face of the bit, a master spline and groove are preferably provided so that the bit and sonde housing fit together in one predetermined alignment. As described hereafter, the splines may be provided on the outside of the projection, and the grooves may be provided on the inside of the socket.
According to a preferred form of the invention, the improved joint comprises a projection extending from a front end portion of the locating device housing, which projection has a series of longitudinal, spaced splines thereon. The projection has a longitudinal axis which is offset from a longitudinal axis of rotation of the drilling head. A rearwardly opening socket formed in the drilling head has longitudinal, spaced grooves configured to receive the splines of the projection therein. A keying mechanism, such as the master spline and groove combination described above, is provided on the projection and the socket to permit insertion of the projection into the socket only in one (or a limited number of) predetermined orientations. Openings in the socket and projection are configured to receive a removable retainer, such as a rolled pin, for mechanically interlocking the projection in the socket with the splines of the projection inserted into corresponding grooves of the socket. Such a joint according to the invention is protected from abrasion because of its location away from the outer periphery of the head, provides a strong connection due to the substantial length and width of the splines, yet can be taken apart easily by manually removing the retaining pins.
In another aspect, the invention provides a cutting bit with a plurality of cutting teeth raked into the cut of the drilling bit. Such teeth are oriented at an angle of at least about 30 degrees relative to an imaginary line normal to an arcuate front surface of the cutting bit from which the cutting teeth project. Such an arrangement provides the desired shear cutting force against the rock face while simultaneously reducing the shock and vibration applied to sonde housing and the drill string. Preferred teeth for cutting rock according to the invention comprise a cylindrical base into which a carbide cutting tip is press-fitted or preferably brazed. These rock cutting teeth preferably have sufficient strength and width to survive and protect the tip from breaking away, plus sufficient length to project beyond the diameter of the brow, so that the teeth and not the body of the bit does the cutting. In a preferred embodiment, a small carbide rod can be inserted behind the tip to act as a back-up tooth when the carbide tip breaks away, as described further below. The cutting teeth are readily replaceable by tapping a used tooth out from behind using rearwardly opening tap-out holes provided for that purpose.
An improved drilling bit according to the invention may further incorporate a rear, frustoconical crushing surface that defines a space or zone crescent-shaped in cross-section that narrows from front to rear. The crescent-shaped crushing zone extends nearly 360 degrees and is configured for crushing rock fragments torn loose by the cutting teeth mounted on the front of the bit. The rear portion of the bit defining the crushing zone is free of large rounded projections that tend to cause loose stones and fragments in the crushing zone to bounce around, rather than be drawn into the narrowing end of the crescent for crushing.
The invention further includes an improved tooth for use on a rock drilling bit. Such a tooth includes a generally cylindrical tooth holder having a first frontwardly opening hole and a second frontwardly opening hole behind the first hole. A first cutting tip fits to a predetermined depth in the first hole. A second cutting tip fits to a predetermined depth in the second hole, such that the second cutting tip is positioned behind the first cutting tip. The second tip preferably is a separate piece from the first, and may have a smaller diameter than the first tooth such that it has a lower cost but is suitable for finishing a bore in progress when the first tooth breaks off.
In another aspect, the invention provides an apparatus for mounting an electronic device therein for use in an underground boring machine. Such an apparatus includes an elongated housing having means at opposite ends of the housing for connecting the housing to other components of the boring machine and an elongated internal chamber configured to receive an electronic device such as a sonde therein and having an elongated access opening which extends along an exterior surface of the housing. A cover sized to close the access opening has edges that fit beneath one or more flanges of the housing. A retainer such as a roll pin is sized for insertion into openings in the cover and housing, which openings become aligned when the cover is positioned with the edges beneath the flange of the housing. The retainer can be compressed from a relaxed state diameter to a retaining diameter at which an outer circumferential surface of the retainer tightly engages inner surfaces of the openings and holds the first part in engagement with the second part.
According to a preferred embodiment, the access opening has a recessed rim including a pair of elongated sides and a pair of ends spanning the sides, each side including a step on which the cover rests when its covers the access opening, and a pair of laterally inwardly extending rim flanges on opposite sides of the access opening each having a pair of inclined undersurfaces, which undersurfaces taper in a direction laterally inwardly and upwardly away from the step. The cover has a pair of laterally outwardly extending cover flanges on opposite side edges of the cover, which cover flanges taper in a direction laterally outwardly and downwardly so that the cover flanges mate slidingly with the undersurfaces of the rim flanges, whereby upon placement of the cover into engagement with the step in a first position wherein the cover flanges and the rim flanges are offset, the cover may then slide in a lengthwise direction so that the cover assumes a second position wherein the cover flanges underlie the rim flanges and at which second position the means for releasably securing the cover may be engaged.
An improved sonde housing according to the invention makes use of strategically positioned hard, wear-resistant studs to protect the body of the sonde housing from abrasion. Such studs have been previously used on cutting bits, but the benefits of using studs on the sonde housing have not been appreciated. In particular, placement of studs on the top face of the housing and optionally in a pair of annular formations near the front and rear ends of the housing improve the service life of the housing. In one aspect, a sonde housing configured for mounting a sonde therein comprises a cylindrical steel body have a sonde-receiving recess therein. A portion of the sonde housing body that receives a reaction force from a cutting bit has a series of hard, wear resistant studs mounted thereon effective to reduce wear on the portion of the sonde housing body that receives the reaction force. In another aspect, portions of the sonde housing body proximate opposite ends of the body have hard, wear resistant studs mounted thereon effective to reduce wear on end portions of the sonde housing body.
A further feature of the invention provides a coupling for a connecting two parts of a machine that rotates about an axis of rotation in use. Such a coupling comprises a first part of the machine that rotates in use, which first part has an first opening having a lengthwise axis which lies in a plane substantially perpendicular to the axis of rotation of the machine, a second part of the machine that rotates in use, which second part has a second opening therein having a lengthwise axis which lies in a plane substantially perpendicular to the axis of rotation of the machine and which is brought into alignment with the first opening when the first part is disposed next to the second part, and a retainer such as a roll pin which is sized for insertion into the aligned openings, wherein the retainer can be compressed from a greater relaxed state to a retaining diameter at which an outer circumferential surface of the retainer tightly engages inner surfaces of the openings and holds the first part in engagement with the second part. Such a coupling can maintain the two machine parts, such as a bit-sonde housing or sonde housing-starter rod, in mechanical engagement even without use of splines for passing torque. The recessed position of the resilient retainer during use shields it from surface abrasion, a common failure mode for bolts and other fasteners that must present an outwardly facing head. These and other aspects of the invention are described in detail below.